How can I understand The Declaration of Independence of Thomas Jefferson? What is the content of this work?

BASIC structure of the Declaration:

1) prologue - addressed to 'the world' , the underlying justification for this declaration, based on the theory that goverments are established by the consent of the governed and to protect their rights, and that a people can, indeed must, replace a govt that continually refuses to honor those rights. The argument is that the King's abuses have forced the colonies to respond by changing their govt.

2) body - list of "grievances" (see breakdown below) mainly listing actions of King George against the colonies, violating their historic RIGHTS

3) final resolution - actual "declaration"

4) closing solemn oath - representatives pledge themselves ('our lives our fortunes and our sacred honor') to defend this delcaration, signing their names

But to understand both structure and contents of this document you must recognize that it is NOT completely original.

Rather, Jefferson was following established patterns and borrowing ideas & expressions from a long history of British & American political documents.

Note esp
1) the "English Bill of Rights" 1689, in which Parliament justified its 'changing governements', replacing James II with William & Mary ("the Glorious Revolution") based on violations of theri rights as Englishmen.

That document begins with a list of the abuses
http://www.yale.edu/lawweb/avalon/england.htm

2) "Declarations and Resolves" October 14, 1774 - the FIRST Continental Congress - listed complaints (simliar to the "abuses" of the Declaration) and called on the King to respond.
The meat of that document begins:
***"do, in the first place, as Englishmen, their ancestors in like cases have usually done, for asserting and vindicating their rights and liberties, DECLARE,
That the inhabitants of the English colonies in North-America, by the immutable laws of nature, the principles of the English constitution, and the several charters or compacts, have the following RIGHTS:***
Resolved, N.C.D. 1. That they are entitled to life, liberty and property: and they have never ceded to any foreign power whatever, a right to dispose of either without their consent. . . .
http://www.yale.edu/lawweb/avalon/resolves.htm

The Declaration's *three* sets of grievances
A) first set -TWELVE charges, beginning with "He has refused his Assent to Law. . . ." ending with "He has affected to render the Military independent. . . ."

B) second set introduced by the following statement --"He has combined with others to subject us to a jurisdiction foreign to our constitution, and unacknowledged by our laws; giving his Assent to their Acts of pretended Legislation:"
This is not a separate charge but the setup for NINE specifics, from "For quartering . . . ." to "For suspending our own legislatures" (Note that this set of charges included Parliament in the indictment, but carefully avoids acknowledging that body, even so much as by naming it!)

C) third set --FIVE more charges, beginning with "He has abdicated. . . " and ending with "He has excited domestic insurrections. . . "

Thus we have a total of 26 specific charges (some count 27 by including the "intro" of B).

For an EXCELLENT treatment of the list of grievances (how were they structured, the sources for Jefferson's original draft, etc) see Paula Maier's book *American Scripture: Making the Declaration of Independence*, pp. 105-23.